This invention relates generally to an apparatus for mounting a draft safeguard switch in a multi-poise furnace.
As disclosed in the Gable et al. U.S. Pat. No. 4,401,425, control devices for shutting down gas fired furnaces in the event the flue gas venting system becomes clogged are known in the art. In the Gable et al. patent, flue gases from a collector box are moved by a fan or blower into a second discharge box and then exhausted into a vent pipe. A baffle is used to direct the flue gases from the blower to the vent pipe to create a negative pressure within the discharge box and thus provide for a natural draft in the flue system.
A draft safeguard switch (DSS) is attached to the side of the discharge box and includes a chimney-like connector through which ambient air is drawn into the discharge box during normal operations. If a pressure above ambient pressure builds up in the discharge box, because of a fault in the venting system, flue gases are forced out of the discharge box through the connector, thereby raising the temperature in the connector. A temperature sensitive switch is attached to the connector which opens when a threshold temperature is sensed which, in turn, shuts down the furnace and the fuel supply valve.
Although the DSS system described in the Gable et al. patent works well in practice, it does not lend itself readily to use in multi-poise furnaces where the furnace can be oriented in a number of different positions that require the flue pipe to be correspondingly reoriented. As noted, the system disclosed by Gable et al. includes a fixed baffle which is needed to create a negative pressure within the discharge box so that the flue gases can flow naturally into the vent system. Although many of the prior art systems operate well in practice, the overall sensitivity of the devices in detecting a restriction in the vent system of a gas fired furnace is generally lower than desired.
It is therefore an object of the present invention to improve apparatus for shutting down a furnace in the event the furnace vent becomes blocked.
It is a further object of the present invention to provide a draft safeguard system that can operate effectively in multi-poised furnaces regardless of the furnace orientation.
A still further object of the present invention is to increase the sensitivity of a draft safeguard system used in a gas fired furnace.
These and other objects of the present invention are attained by draft safeguard systems for use in a multi-poise furnace having an inducer box located at the outlet of the furnace heat exchanger. A vent pipe is attached to the inducer housing by an elbow having a linear inlet section that is rotatably connected to the inducer box and a linear outlet section connected to the vent pipe. The two linear sections of the elbow are, in turn, connected by means of a bend section. The elbow can be rotated within the collector box to different positions, depending upon the furnace""s orientation. An elongated flue gas sensor housing is mounted upon one section of the elbow and contains a first opening that communicates with the flue gas flow within the elbow and a second opening that communicates with the surrounding ambient. A temperature sensing limit switch is mounted upon the sensor housing adjacent to the second opening for sensing the temperature of the flow moving through the sensor housing between the openings. Under normal furnace operations, ambient air is drawn into the inducer box through the sensor housing. In the event of a vent blockage, the flow is reversed and hot flue gases pass over the limit switch cycling the switch and shutting down the furnace.
A baffle is mounted with the elbow over the flue gas inlet to the sensor housing. The baffle establishes a chamber over the inlet that is closed at one end, that faces the flow of flue gas that enters the elbow from the inducer unit. The opposite end of the baffle is opened to a reversal of flow in the vent system in the event of a restriction in the system.